This invention relates to a universal joint of the Hooke's type, hereinafter referred to as a Hooke's joint.
A Hooke's joint comprises two yoke elements which in use rotate about respective axes (hereinafter called the rotary axes), these rotary axes coinciding in the straight position of the joint. Each yoke element includes a base portion and a pair of arms projecting axially from the base portion at diametrically opposite positions with respect to the rotary axis of the yoke element. The joint further comprises a connecting member pivotally connected to the arms of one yoke element and to the arms of the other yoke element for movement about respective mutually-perpendicular pivot axes which, in the straight position of the joint, are also perpendicular to the rotary axes of the yoke elements. The shafts or other rotary elements which are required to be coupled through the intermediary of the joint are integral with or connected to the base portions of respective yoke elements.
A common construction of Hooke's joint includes yoke elements, each of which has a pair of aligned circular openings formed one in each arm of the element, bearing cups in these openings, trunnions provided on the connecting member and received in respective ones of the bearing cups and needle bearings interposed between the trunnions and the bearing cups. Four retaining elements are provided, one on each arm of each yoke element, to retain the associated bearing cups within their respective openings.
It is desirable to avoid movement of the connecting member relative to either of the yoke elements in a direction along the pivot axis of that yoke element. Such movement will cause wear of components of the joint and will enable the centre of gravity of the connecting member to move from the rotary axis of one or both yoke elements so that the joint is out of balance. Rotation of a Hooke's joint in an out of balance condition generates vibration which can give rise to serious wear and to excessive generation of noise.
When the components of Hooke's joints are formed in a reasonably economical manner, it is inevitable that the dimensions of the components will vary within acceptable tolerance ranges. The existance of such variations gives rise to difficulty in avoiding freedom for movement of the connecting member relative to the yoke elements along the pivot axes thereof.